Radiation and radioactivity were discovered more than 100 years ago. Since then, advances in technology and a better understanding of its effects on the body have made radiation therapy an important part of cancer treatment. In fact, more than half of all people with cancer will get radiation as at least part of their cancer treatment.

What is radiation therapy? When is it used?

Radiation therapy uses high-energy particles or waves, such as x-rays, gamma rays, electron beams, or protons, to destroy or damage cancer cells. Other names for radiation therapy are radiotherapy, irradiation, or x-ray therapy.

Radiation therapy is one of the most common treatments for cancer. It is often part of the main treatment for certain types of cancer, such as cancers of the head and neck, bladder, lung, and Hodgkin disease. Many other cancers are also treated with radiation therapy. Thousands of people become cancer-free after getting radiation treatments.

"Radiation can be given alone or used with other treatments, such as surgery or chemotherapy," says Philip Maddock, MD, radiation oncologist at Kent Hospital.

"In fact, certain drugs are known to be radiosensitizers. This means they can actually make the cancer cells more sensitive to the radiation, which allows the radiation to better kill cancer cells. There are also different ways to give radiation. Sometimes a patient gets more than one type of radiation treatment for the same cancer."

How does radiation therapy work?

All cells grow and divide to form new cells. But cancer cells grow and divide faster than many of the normal cells around them.

Radiation therapy uses special equipment to deliver high doses of radiation to the cancer cells. This damages cancer cells and causes them to die. Radiation works by breaking a piece of the DNA molecule inside the cancer cell, which keeps the cell from growing, dividing, and spreading. Nearby normal cells also may be affected by radiation, but most fully recover from the effects of the treatment and go back to working the way they are supposed to.

Unlike chemotherapy, which exposes the whole body to cancer-fighting drugs, radiation therapy is usually a local treatment. It is aimed at and affects only the part of the body. The goal of radiation treatment is to damage as many cancer cells as possible, with little harm to nearby healthy tissue.

Some treatments involve radioactive substances that are given in a vein or by mouth. In that case, the radiation does travel throughout the body. But for the most part, the radioactive substance collects in the area of the tumor so that there is little effect on the rest of the body.

Do the benefits outweigh the risks and side effects?

Radiation therapy may be more helpful in some cases than in others. For example, some types of cancer are more sensitive to radiation than others. And some cancers are in areas that are easier to treat with radiation without causing major side effects.

There are lifetime dose limits of radiation. Doctors know the amount of radiation that normal parts of the body can safely get without causing damage that cannot be reversed. They use this information to help them decide how much radiation to give and where to aim radiation during treatment. If a part of your body has been treated with radiation before, you may not be able to get radiation to that area a second time. This depends on how much radiation you got the first time. If one area of your body has already gotten the maximum safe lifetime dose of radiation, you might still be able to get radiation treatment to another area if the distance between the two areas is large enough.

What types of radiation are used to treat cancer?

If your doctor recommends radiation treatment, it is because they feel that the benefits you may get from it will outweigh the possible side effects. Still, this is something you must be comfortable with. Knowing as much as you can about the possible benefits and risks can help you decide whether radiation therapy is best for you.

Radiation therapy can be given in 3 ways: as external radiation, as internal radiation, or as systemic radiation. In some cases more than one type is used.

External radiation (or external beam radiation) uses a machine that directs high-energy rays from outside the body into the tumor and some normal nearby tissue. Most people get external radiation therapy over many weeks. It is done during outpatient visits to a hospital or treatment center.

Internal radiation therapy (also called brachytherapy) uses a radioactive source in the form of a wire, seed, pellet, or balloon that is called an implant. The implant is put inside the body in or near the tumor. The radiation from the implant travels only a short distance, so it has very little effect on normal body tissues. In some cases, patients may need to stay in the hospital while getting internal radiation.

Sometimes, after a tumor has been removed by surgery, radioactive implants are put into the area where the tumor was to kill any cancer cells that may still be there.

Implants may either be left in the patient as a permanent implant or they may be removed after a certain amount of time.

Systemic radiation is given using radiopharmaceuticals, which are radioactive drugs used to treat certain types of cancer. These drugs are unsealed radioactive sources that can be given by mouth or put into a vein; they then travel throughout the body. Treatment with radiopharmaceuticals often requires a short stay in the hospital.

Deciding which type of radiation to use depends on the kind of cancer you have and where it is in your body.